1. Field of the Invention
The present invention relates to a coating method and an atomizer, and more particularly to a coating technique using supersonic vibration.
2. Related Background Art
Some types of atomizers are currently known. They are rotary atomizers configured to atomize a coating material with a bell-shaped rotating member driven at a high speed, spray type atomizers configured to atomize a coating material by expelling it together with air from a nozzle, and hydraulic atomizers configured to atomize a compressed coating material by extruding it from a minute opening.
Rotary atomizers, in general, have a bell-shaped cup at one end of a rotary shaft of its main body as disclosed in Japanese Patent Laid-open Publication JP-H03-101858-A (equivalent to Japanese Patent No. 2600390), for example. A coating material supplied to the bell-shaped cup from a paint supply pipe spreads in form of a thin film along the inner surface of the bell-shaped cup radially outwardly under the centrifugal force, and it is next atomized while flying outwardly from the outer circumferential perimeter of the bell-shaped cup. Then, a shaping airflow drives the atomized coating material forward toward a work to be coated.
A known problem with rotary atomizers is irregularity of the grain size of the atomized coating material. Distribution of grain sizes includes two major peaks, i.e., one peak of a relatively large grain size and the other peak of a relatively small grain size. Irregularity of the grain size of the coating material invites instability of the film quality and degradation of the deposition efficiency of the coating material. This problem is known to occur in spray type atomizers and hydraulic atomizers as well.